I'm developing a magic system for a forged in the dark hack. It's based around ash as the remnants of magic

So the basic concept is that magic is found in the most random places. And you'll never know it's there until you burn it down. Basically, ash that burns in the presence of magic is a vivid to dark blue. It is also noticeably lustrous.

But that is besides the point.

Magic in this world comes from ingesting ash in various ways. Simple magic is achievable by almost anyone. The process is simply to chew on this blue ash until it warms up, then expelling it as a smoke that can act on your behalf. It can carry out simple tasks or deliver messages to nearby allies. Obscure your surroundings so keep you unseen or even lightly burn something or someone.

However, this comes at the cost of a level-one harm. Maybe your lips are burt or your mouth blisters. Maybe your tongue swells or your teeth crack. Regardless, the damage shall not be prevented.

Then there are those that use ash more regularly. These mages have developed an immunity to the harm over time, but have developed a more severe habit. Instead of just chewing on the ash, they swallow it. Having it build up in their body to allow them short bursts of magical power. The ash is tempered by breathing and straining the body. Any magic requires taking at minimum two stress. And if you exceed your limit of stress the magic will run wild and you will gain a permanent disfigurement.

But the power you might weild is worthy of risk.